I'm trying to use lilypond to create some guitar neck diagrams for memorizing intervals and scale patterns. I can use fretboard-diagram-verbose to place it in landscape orientation, extend it to as many frets as I need, etc. I now have some charts which are very nice, but I notice that the fretboard engraver renders each fret as the same size, and I'm trying to figure out if it would be possible to instruct lilypond to render the leftmost frets to be wider than the rightmost frets (as it actually appears visually on a guitar neck).
I don't see any attributes in fret-diagram-details that would enable that functionality. I see in the internals reference that I can customize the stencil, which is fret-board::calc-stencil by default. Would writing a custom stencil be the best way to accomplish this? If so, is there any guidance as to how one actually writes a custom stencil. I can see that the notation reference manual has a section on modifying stencils, but the example given only substitutes one stencil in place of another. Is there any documentation on how to actually go about writing a stencil from scratch?